Add some sort of contact_email field to server.json

I think it would be helpful to encourage (or require?) publishers to include a contact email when publishing a server.

This would empower at least a few downstream functionalities for us:

1. Notify the MCP Registry userbase of major changes/announcements. For example breaking changes or database wipes, especially while in Preview.
2. Automated checks that ensure server.json data is valid / working, and automatic takedown (with notification) in the case that something is nonworking

In particular I expect (2) is going to quickly become a problem, whether intentionally or unintentionally I expect many server.json's to have typos and other bugs. And if MCP Clients can't rely on us to serve working data, they won't use us as a source of truth. I'm not sure yet if it's necessary to solve this at the centralized layer (maybe sub-registries could handle it), but having email addresses for notifications would at least make this conceivable to manage. Otherwise we would be modifying/taking down server entries with no feedback loop back to the publishers.

Start with the server.json schema and the issue's proposed contact-email use cases. Clarify whether the field should be encouraged or required, which publisher notifications it supports, and what validation or takedown behavior would count as complete.